Method for reducing cross talking in telephone phantom lines



' Jan. .1925. 1 523,299

E. SCHURER METHOD FOR REDUCING CROSS TALKING IN TELEPHONE PHANTOM LINES Filed Dec. 8, 1923 5heets-Sheet 1 L z m 3 T2 4 E I102) eniiaz 21501312,]: 612

E. SCHURER METHOD FOR REDUCING CROSS TALKING IN TELEPHONE PHANTOM LINES I 2 Sheets-Sheet 2 Filed Dec, 8, 1923 @022 elm/E 1 Patented Jan 13, 19235.

FFC.

EUGEN SCI-IIIRER, OF GOLOGNE-MULHEIM, GERMANY.

Application filed. December 8, 1923.

To all whom it may concern:

Be it known that I, EUGEN ScrIt'mER, a subject of the German Republic, and residing at Genoveva Strasse 68, Cologne-Mulheim, Germany, have invented a certain new and useful Method for Reducing Gross Talking in Telephone Phantom Lines, of which the following is a specification.

This invention has reference generally to improvements in telephone systems and more particularly relates to a method for reducing cross-talking in telephone phantom lines.

The invention as its primary aim and obj ect consists of a method in which adjustable impedances are employed for determining the balancing impedance and subsequently substituting therefor balance impedances preferably in the form of chain conductors arranged in series with and between the lines to be balanced and the apparatus at the end thereof while the other ends are short circuited or closed through suitable resistances, the chain conductors being arranged in such manner that the dependence of the real and imaginary parts of the impedance of the chain conductors are dependent upon the frequency in the same manner as the value of the corresponding parts of those found in the previously used adjustable impedances.

Other objects as well as the nature, characteristic features and scope of the invention will be more readily apparent from the foregoing description taken in connection with the accompanying drawings and pointed out in the claims.

Figs. 1 to 3 illustrate the manner in which phantom lines have previously been balanced.

Fig. 4 illustrates the method. for balancing lines which constitutes my invention.

In Figure 1 of the accompanying drawings the one end of the phantom line constituted by the main lines (1, 2) and (3, 4c) is connected to the apparatus 1, II and III, the apparatus I and II being used for the two main lines and the apparatus III for the phantom line. The two ends of the latter apparatus are connected to the symmetrical centres of the transformers T and T The disturbance caused in the apparatus I and II by the currents derived from the apparatus III, viz, cross-talk, is due to the Serial No. 679,5 13.

impedances of the branches of the pairs of conductors, considered from the centre of symmetry of the line, being different in consequence of asymmetries of capacity and inductance, so that from the points of connec tion of the apparatus III with the trans formers the two halves of the latter are traversed by currents of different amplitude and phase.

In order to avoid this disturbance, use is at present being mainly made of a method by which the inequalities in the capacities and inductances of the conductors are balanced within or between certain sections of the line, during the installation of the latter, whereby the impedances of the branches of the line at the ends thereof are made practically equal.

However, cases are encountered in practice, for instance in submarine telephony, in which a subsequent balancing of the lines in sections is not possible. In order to reduce cross-talk in these cases it has been proposed to effect the balancing of the ends of the lines by first of all connecting the ends of the lines to earth through impedances as indicated in Figure 2, each impedance consisting of a resistance R connected in parallel with a capacity K, and by adjusting the resistances and capacities for the individual frequencies within the range of frequencies of the balancing to such values that for the adjustment corresponding to each frequency the total impedances connected to the two halves of the transformer become equal to each other, which was indicated by the disappearance of the crosstalk disturbance at the particular frequency. Some of the values of the resistance and capacity ob" tained by these adjustments vary considerably with the frequency. In order to reduce talk in the whole range of frequency, the resistances and capacities would have to be replaced by impedances, the real and imaginary parts of which are dependent upon the frequencies in the manner indicated by the adjustment of the resistances and capacities.

However, it has hitherto been impossible to produce such impedances, for which reason only the greatest deviations of the adjusted values from their mean values were taken into consideration and use was made but of a series This method eliected a very ilnmsurate balancmg. In addition thereto the eartlnng at the ends of the line over the comparatively small resistances of these end connections had also certain technical disadvantages.

It has been endeavored to avoid these disadvantages by inserting the adjusted or balance in'ipedances in series between the ends of the lines and the apparatus provided at the ends of the lines (ttrmisformers). F or this purpose use has been made of adjusted impedances which, as shown in Figure 3, consist of an adjustable resistance? and an adjustable self-inductance L (variometer). By adjusting these adjustable members so thatthey shall cause the cross-talk to be practically negligible for every frequency, we obtain those real and imaginary additional values; by which the components of the impedances of the two branches of the line -are completed to equal values for the individual frequencies.

In order to obtain balance impedances which are to be used in the place of the adjusted impedances and the real and imaginary parts of which depend upon the frequency in the same manner the adjusted valuesof the resistance and self-inductance, it is assumed, according to theinvention, that the irregularities in the impedance of the branches of the line producing the crosstalk have to be considered as being caused by additional irregularities being superposed upon uniformly distributed properties of the lines and that these irregularities by themselves may. be considered as an irregular artificial line, whichat its inlet terminals shows that the real and imaginary parts of its impedance are dependent upon the frequency-in a manner which is substantially complementary to the manner in which the adjusted resistance and self-iinluctance of the adjusted impedances are dependent upon the frequency. According to this, the adjusted impedances can be imitated as regards the manner of their dependence upon the frequency by irregular artificial lines, which can then be substituted for the adjusted impedances.

According to the invention use is made of balance impedances, which, as shown in Figure at, are connected with their inlet terminals (4 b in the place of the previously used adjusted impedances in series between the lines and the apparatus at the ends thereof, and which are short-circuited or'closed over suitable resistances at their rear'ends.

The form of these chainl conductors is immaterial and any of the well-known arrangements of chain conductors 'may be used. The number and irregularity of the members and member elements of these chain conductors are so chosen that the dependence of the real and imaginary part of the impedance of the chain conductors on-the frequency follows a curve, which is identical with or similar to that found for the corresponding parts of the adjusting impedances when adjusted. a

The artificial lines referred to may be of any form;.any known arrangement of artificial line may be used-for the purpose of the present invention. In the arrangement illustrated, by way of example, in Figure 4, the

artificial lines used as'balance impedances comprises three members each of which con sists of a self-inductance (for instance Z Z Z 7/ Z or l and a capacity (for instance 70 k is k 7s or 72' "The required-nunr bers of. members and theirequired values for theindividual Z Z, and]! lc are irst of all found out in an artificial line having a variablemunber of members and adjustable Z and 71? by varying them until the real and in'iagiuary parts of the impedance of the artificial line show that they are depend ent upon the frequency in substantially the same manner as w as previously ascertainedl the adjustment of the adjusted impedances. The fixed artificial lines to be inserted as balance impedances-are then constructedfor each line in such a manner that the number 3 1 of their members and the values of Z and 7c are the same as those found with the adj ustable artificial line. 7

lVhat I claim is: 7'

A method of balancing telephone phantom lines for reducing cross-talking consistmg in determining by adjustable impedanees the desired balance lmpedance and substitutmg a plurality of chain conductors 1n series with the lines in sucha manner that the EUGEN sonnets. 

